Process of preparing cycijc esters



Patented YSept.k 7, 1.937

UNITED STATES PATENT [OFFICE PRooEss orv PREPARTNG cromo EsTEas Edgar W. Spanagel, Wilmington, Del., assigner to E. I. du Pont de Nemours &. Company,`-Wil mlngton, Del., a corporation of Delaware Application March 12, 1935, Serial No. 10,637

9 Claims.

This invention relates to cyclic esters, particularly those having rings of more than seven atoms, and processes for making the same. More I-IOCHzCHzCHzCOOl-I gives butyro-lactone and monomeric ethylene carbonate,

is readily obtained by the action of diethyl carbonate or of phosgene on ethylene glycol); and it might be supposed that cyclic esters having rings of more than seven atoms would be obtained from appropriate open chain compounds in the same Way. But in fact, they cannot be obtained in `this Way. Extensive study (J. Am. Chem. Soc. 51, 625, 2560, 3450 (1929) 52, 314, 711, 3292 (1930); Helv. Chim. Acta 12, 463 (1929)) has shown the reason for this is that the ester formation proceeds intermolecularly and yields polyesters of high molecular weight.

Thus, hydroxydecanoic acid, I-IO(CH2 9COOH, undergoes self-esterication When it is heated; the product, however, is a polyester of the general formula Ho cH2 gco-,oroHn goo-own@ gooo-(CHZ) goo-H.

and no discoverable amount of the corresponding cyclic lactone,

[i0 (CHM C O-l (c1. 20o-12s) and not as a monomeric cyclic ester,

Again, hexamethylene carbonate is obtained as and'not as |:o (Crim ooo-:I

Forthe purpose of further discussing some. of the above compounds it is convenient to. intro' lduce and dene certain terms. The polymeric esters preparedor derived from hydroxy acids or from dibasi acids and glycols are called'linear polyesters. The molecules are long chains having a structure that may be symbolized by the general formula,

-ORCO-ORCO--ORCO-ORCO-ORCO- ORCO-.

(R is not necessarily a hydrocarbon residue. The

length of the molecules andthe nature of the 2 Name of ester Formula of structural unit lgltl Ethylene succinate 8 Ethylene carbonate. Dccamethylene carbonate. 13

. Self-ester from w-hydroxy- 1 1 'decanoic acid.

The unit length is obviously Adefined by the nature of the compounds from which the ester is derived. It is the same as the number of atomsthat Would be present in the ring of the monomerio cyclic ester if such an ester could be obtained. In general, this unit length determines the nature of the es ter that will be produced. If the unit length is ve or six,fa cyclic monomeric ester is readily obtained; if the unit length is more than seven, the product is alinear polyester.` These generalizations apply to esters derivedfrom hydroxy acids or from dibasic acids plus `dihydric alcohols, whether the esters are prepared from these reactants as such or from appropriate derivatives of these reactants.

Linear polyesters are either solids or highly viscous liquids. They are non-volatile and stable and they generally show little or no tendency to break down under the inuence of heat until a very high temperature is reached (e. g., 300 C. t0 5 500 C.) and the reaction that then occurs-is not simple depolymerizatonA but destructive thermal decomposition: carbonaceous, tarry, gaseous, and liquid products are formed. From the latter it is sometimes possible to isolate very small amounts of cyclic esters (true depolymerization products of the polyester used): dimeric cyclic esters have thus been obtainedfrom ethylene succinate, tetramethylene carbonate, and tri.

methylene oxalate; but the process is not general; the yields are very poor; and no monomeric cyclic esters having more thanseven atoms in the ring have ever` been obtained by this method.

This invention has as an object the preparation of cyclic esters having at least seven members in the ring by an improved process. A further object is the provision of a simple and rapid method for the depolymerization of linear poly- 'esters'. A still further object is the provision of catalysts whereby this reaction is rendered more feasible and economical. A still further object is the preparation of new and useful odoriferous compounds. Further objects will .appear hereinafter.

These objects are accomplished by the following invention, wherein a linear polyester is heated ence of a basic catalyst under conditions whichv permit the removal of the volatile products as they are formed. This method gives satisfactory results with esters derived from carbonio, oxalic,

and malonic acids, but less satisfactory results with esters derived from higher acids of. the

series, such as succinic, glutaric, se'bacic, etc., bev 50v cause of the slow rate of depolymerization ofthe It is likewise less satisfactory.l for the preparation of cyclic-esters' from poly-J.

linear polyester.

esters derived from hydroxy acids.

It has now been found that the chlorides,A nitrates, carbonates, and oxides of magnesium,

manganese, iron, cobalt, and tin (all in the divalent state) are much more powerful and effective catalysts for the depolymerization of linear poly. esters than the basic"`compounds previously 4cliscio-sed. 'I'he use ofthese new catalysts renders possible the rapid depolymerization of linearl polyestersderived from succinic, glutaric, andhigher members of the dicarboxylic acid series and thus makes possible the preparation ofmany .65 membered cyclic esters, hitherto obtainable only with the greatest. of difficulty, in good yields, ranging from 40% to 80%. These catalysts are also useful in thedepolymerization ofpolyesters derived from lower dibasic acids,.such as car- I 7,0 bonic, oxalic, and malonic acids, and in the depolymerization of polyesters derived from .hydroxy acids. In addition to being more effective catalysts than the basic compounds'previously disclosed, catalysts of the present invention give a much higher ratio of monomer to dimer, which `more pronounced odor and is of greater-value/as is desirable since the cyclic monomer 'has the l l a perfume ingredient. l

The invention, therefore, consists in depolymenizing linear polyesters in the presence of a cata-51's lyst of the class mentioned. The preparation g-j of the linear polyester'is not a part of the pres-1f4 ent invention, and polyesters prepared 'by any@- method may be used. A suitable method for thel preparation of linear polyesters from glycols and]I {10 dibasic acids consists in heating substantially -f equimolecular quantities o f glycol and dibasic l acid at -200 C. for several hours and then heating the resultant mass for a few more hours at 200 C. under 2 mm. absolute pressure. Esters 15 of the dibasic acid may also be used in the prep. aration of the polyesters, and in this case it is, sometimes desirable to carry out the reaction in the presence of a small amount of sodium or other ester interchange catalyst. It is desirable 20 -to prepare the polyester' with a small excess of glycol, since polymers -prepared'in this way seem to depolymerize more readily. Polyesters can be the formation -of many membered cyclic esters is effected by heating the polymer under reduced pressure below' 10 mm. and preferably below l mm., absolute pressure, in the presence of a small" .35 amount of catalyst taken from the class above named. Generally, from-f0.1 to'1.0% of catalyst is used, but larger amounts are not harmful. The polyester-catalyst mixture may be prepared by simple admixture or by incorporating the cata- 40 lyst in the polyester during its preparation. A molecular still may be used for the depolymer' ization, but with the catalysts herein described ordinary distillation equipment is usually satisfactory. An apparatus which has proven es.- 45

pecially useful for this purpose is that illustrated in the accompanying s'llre.

. A'I'he polyester and catalyst are placed in A,

which is fitted to a dephlegmator E and a receiver AD. D is connected with a pump capable of evac- 50 uating the system to less than 1 mm. pressure. The content of A is then heated to the depolymerization temperature by the vapors in C, which arise from a suitable liquid `vigorously boiled .in B. The liquid in B is chosen so that its boiling 55 temperature is suiliciently high to cause depolymerization of the polyester but not high enough to cause destructive thermal decomposition. The difference between depolymerization and thermal decomposition is important as shown above. 00

Temperatures of 150- 375 C. are` used, the preferred range being 2 50-275 C. When necessary the ratio of monomer to dimer may be greatly increased by the use of reflux made possible by-4 the dephlegmator E, which is cooled by steam or 55 other suitable -vapor or liquid. This is highly desirable, inasmuch as the monomeric cyclic esters are the most useful, at least as far as perfume ingredients are .concemed. The apparatus described in'the figure may-be constructed of 70 glass or other suitable material.

'- 1 This invention has greatly extended the ileld V of synthetic possibilities. A host of cyclic esters can be prepared by depolymerizing polyesters derived from various combinations of dibasic acids. 15

and glycols.. One hundred monomeric cyclic esters alone may be obtained from a group of ten acids and ten glycols. A large number of polyesters may also be prepared from hydroxy acids.

Table I includes a list of new cyclic esters Aprepared by the method of this invention.

TABLE I New cyclic esters Cyclic ester Ring M. P. (M=mcnomcr; D=dimcr) size C./xn1n C.

' Ethylene succinate (D) 131 z'lfrimethylene succinate (M)- 81 -Trimethylene succinate (D) 138 Tetramethylene succinate (M Liq. Tetramethylene succinate (D) 121 Pentaniethylene succinate (M) Liq. Pentaniethylene succinate (D) 87 Hexamethylene succinate (M) Liq. Hcxamethylene succinate (D) 110 Heptamethylene succinate (M) 49 Heptamethylene succinate (D 8G Octamethylene succinate (M) 71 Octainethylene succinate (D) 100 Nonamethylcne succinate (M) 15 71 Dccaiuethylene succinate (M) 16 135-140l2 58 Dodecamethylene succinate (M) 18 156150/2 Liq. Tridecamethylcne succinate (M 19 154/1-2. Liq. Oetadecamethylene succinate (M) 24 199-201/2 Liq. Decamethylenc-glutaratc (M) 17 13G-13 Liq. Hexamethylcne adipate (M) 14 117/2 70 Triethylcric (glycol) adipate (M) 16 162/2 50 Nonamethylcne adipatc (M) 17 l44146/2 Liq. Heptamethylenc suberate (M) 17 15S-160] l-2 47 Ethylene azelate (M) 13 52 Ethylene azelate (D) 26 145 Tetramethylene azclatc (M 15 123124/2 Liq. Hexamethylene azelate (M) 17 59 'lrimcthylene scbacatc (M). 15 130l33l2 Liq. Tctramethylene scbacate (M) 16 136-13872. Liq. Pcntamcthylene scbacate (M). 17 159l60/l2. 37 Hcxamethyleue sebacatc (M) 18 47 Dicthylene (glycol) sebacatc (M) 17 150-157/2 Liq.

Ethylene decamethylcne dicarboxylate (M v16 139-141/2 Liq. Ethylene brassylate (M) 17 139142/2 Liq. Decamcthylcne cctadccancdoate (M) 30 G0 Ethylene phthalate (M) 8 160-170/2 55 Ethylene phthalate (D) v16 198 `For the most part the many membered cyclic esters are liquids or low melting solids. The

55 carbonate, nonamethylene adipate, hexamethyl` ene azelate, decajrnethylene succinate, ethylene brassylate, and t-hydroxy pentadecanoic acid lactone. These compounds all have musk-like odors which make them valuable substitutes for 60 the essential principle in musk and civet. In general,the intensity of the odor is greatest Iin the case of the cyclic esters of the lactone type,

i. e., those yderived from-hydroxy acids.

While vboth monomeric and dimeric cyclic es- 65 ters are formedVV when polyesters are depolymerized, the relative amounts of these products vary, depending ehiey upon the experimental conditions and the unit length of the ester. The

, catalysts of the present invention'are more active 70 than those previously described," and favor the formation of monomer. The use of reux as i1- lustrated in the drawing also increases the ratio of monomer to dimer. The eifect of unit length on the ratio of monomer to dimer is shown in 75 Table II, illustrating the results obtained in the depolymerization of a series of polymeric succinate's under identical conditions. In each case 50 g. of polymer and 0.5 g. of hydrated stannous chloride were heated without reflux in a vapor heated still to 268 C. at 1 mm. pressure for four hours. It will be noted from the table that the` dimer was formed almost exclusively in the case of ethylene succinate in which the monomer would be an Sfmembered ring.' whereas the 15- membered monomer was almost the sole product in the case of nonamethylene succinate.

TABLE II Influence of structure of monomer formation,

Size of Polymer lzerrlft mono- Percent lercent merie monomer in icr distillate ring Ethylene succinate 73 8 0 100 'lriiiietliylcne succinate.. 47 9 11 89 lctrametliylcne succi nate 48 l0 79 21 Pentametliylene succin .e 77 1l 74 26 Hexamethylene succiy nato. 73 l2 80 20 Octanicthylene succinate. 81 14 95 5 Nonamethylene succinuto 84 15 100 0 Decametliylene succinate 76 16 100 0 Having outlined above the general principles and purposes of the invention, the following exempliiieations thereof are added for purposes of illustration but not in limitation.

Example 1 'Substantially equimolecular portions of hexamethylene glycol and succinic acid Were heated in a distillation flask to 200 C. for about three hours. 200 C. under two mm. pressure for two hours. 'I'he linear polyester thus formed was not purified but was used in the crude state in the following depolymerization experiment:

A mixture of 50 g. vof crude hexamethylene succinate polymer and 0.5 g. of hydrated stannous chloride was heated at 263 C. under 1A mm. absolute pressure inl an apparatus of the type shown in th figure. The temperature of 268 C. was maintained by thevapors of boiling orthochlorodiphenyl. The polymer soon became soft and bubbled vigorously. In about 10 minutes distillation started, the rates of distillation being as follows:

Drops per minute After 15 minutes 1-2 After 30 minutes 14 After 45 minutes 10 After 60 minutes '8 After 75 minutes 3 After about 30 minutes heating the residue became a stiff porous gel which darkened asthe depolymerization proceeded. After four hours, when distillation had practically ceased, only a small amount of brittle porous mass remained. The distillate obtained consisted of 32 g.. of light yellow liquid and 8 gof white solid. The solid portion on recrystallization from alcohol melted at 110 C. It was the cyclic-dimer. Anal. of dimer: caled. for C2oHs2O=C,60.00%; H,8.00%; mol. wt., 400. Found: C,60.41%; H,8.14%; mol. wt., 393.

The liquid portion of the distillate on redistillation gave 21 g'. of pure cyclic monomer, boil- "ing at 108-110 C. at 2 mm. pressure.v Anal. of

The resultant mass was then heated at monomer: calcd. 118.00% mol. wt., H,8.04%; mol. wt., 199.

The structures of these products are represented below:

Monomer Dmer (l2-membered cyclic ester) (2l-membered cyclic ester) Other cyclic esters prepared by this general 15 method are listed in Table I.

Exemple 2 Decamethylene carbonatepolymer was prepared by heating 43.5 g. of decamethylene glycol with 43.5 g. of butyl carbonate inthe presence of 0.5 g. of stannous chloride to 200 C. during about four hours. Forty-four grams of the polymer thus prepared was heated with 0.5 g. of stannous chloride at 268 C. under 1 mm. absolute pressure for four hours in a vapor heated still of the type shown in the figure. The distillate amounted to g. from which -15 g. of highly pure decamethylene carbonate boiling at 9293 C. at 1 mm. was obtained on fractional distillation. The product was identical with that described by Carothers 5 and Hill in J. Am. Chem. Soc. 55, 5031 (1931).

Other linear carbonates yielded the corre- I sponding cyclic esters when treated in asimilar manner.

40 Example 3 A mixture of 20 g. of hexamethylene sebacate polymer and 0.2` g. of hydrated cobalt nitrate was heated for two hours at about 270 C. under 1 mm. absolute pressure in a glass still of the type illustrated 'in the figure. The distillate (14 g.) was dissolved in 50 cc. of alcohol, cooled in solid carbon dioxide, and ltered. 'I 'he residue (11 g.) consisted of pure monomeric hexamethylene sebacate (IS-membered cyclic ester), melting at 41 C. It has a musk-like odor. Anal. of monomer: Calcdl for C1sH2sO4=C,67.60%2 H,9.85%; mol. wt., 284. Found: C,67.41%; H,9.75 mol. wt., 260.

A wide variety of catalysts'may be used inthe preparation of cyclic esters. The results obtained in ,depolymerizing hexamethylene seba-A cate with la number of these catalysts under conditions identical with those used in Example 3 With'cobalt nitrate are listed in Table III.

pressure for two hours.

' Example 4 A mixtureof 20 g. of w-hydroxydecanoic acid linear polymer, (O-(CI-Iz) 9CO)x, and 0.5 g. of hydrated magnesium chloride was heated in a vapor heated still to 270 C. at one mm. or less absolute l The distillate,- a mixture of white solid and liquid, weighed 13 g. On recrystallization from 50 cc. of alcohol, 9` g. of dimer separated, melting at 95-96 C. The alcohol residue was concentrated and distilled in vacuo. 'One and one-half grams of monomer was isolated boiling at 113-1l5 C. at 15 mm.

Other properties of the monomer arez'melting v point, 6 C.; u

Ng? 1.4655; D343 0.9926. Analysis: calcd. for y Vcwrnlo2= v2fzo-5; H,1o.58.

Found; 0,7031; H,1o.13.

Monomer Dimer (ll-membcred cyclic ester) (ZZ-membered cyclic ester) Example 5 I Fifty-seven grams of the linear polyester obtained from w-hydroxytetradecanoic acid was dey mately one g. of a cyclic dimer and 25 g. of highly pure monomer. The latter had a musk-like odor,

melted atf28 C., boiled at 16S-166 C. at 13 mm., l

and had a refractive indoex of These properties check closely with those reported in the literature for .this compound. (Ruzicka Monomer Dimer (l-membcred cyclic ester) (BO-membered cyclic ester).

Other cyclic esters of the lactone typ-pe can be prepared in the 'same manner. Thus, the 16- `membered pentadecanoic acid lactone can be prepared by this procedure from the polymer of w-hydroxypentadecanoic acid.

Compounds which have proved o f particular value as catalysts for the depolymerization of linear polyesters'are listed in Table III. 'I'hese may be used inthe hydrated orv anhydrous form either alone or in mixture. It may also be mentioned that powdered magnesium may be used.

'I'he process, while of particular value with those catalysts listed in Table III, is applicable generally to the chlorides, nitrates, carbonates and oxides of.magnesium, manganese, iron, cobalt, and tin when these metals are in the divalent state. The following vcatalysts were tested and found ineffectivejn influencing thedepolymerization: zinc fluoride, boron trifluoride, antimony trifluoride, zinc chloride, nickelous chloride, cu-

prous chloride, chromous chloride, chromic chlo- Y,

ride, aluminum chloride, titanium tetrachloride, stannous bromide, antimonyA triiodide, calcium carbonate, ferrous sulfate, magnesium phosphate, potassium acetate, sodium tungstate, sodium vanadate, boric oxide, silicotungstic acid, and potassium phthalimide. Ferric chloride, antimony tril 2,092,031 chloride, thallium carbonate, and thorium nitrate had only a slight catalytic effect. A wide variety -of glycols and dibasic yacids are represented in the cyclic esters described in Table I. 'I'he invention is not limited to the preparation of these particular esters, however. Esters may be prepared from other acids, such as oxalic, methylmalonic, dimethylsuccinic, cyclohexanedicarboxylic, phenylenediacetic, resorcinoldiacetic, and hydr'oqui-` nonediacetic acid. Iny addition to those mentioned in the examples and the tables, esters may be prepared from glycols such'as' ri-dimethyltrimethylene glycol. The case of depolymeriza- .tion varies with the esters. Decamethylene phthalate and .decame'thylene maleate are resistant to depolymerization, as are likewise those polyesters derived from l2hydroxystearic acid and from hydroxycitronellic acid. `In the case of depolymerization of hydroxy acids, those esters l prepared from hydroxy acids having primary hydroxyl groups are preferred, and particularly the w-hydroxy acids.

This invention provides a rapid and efficient method for the preparation of cyclic esters hav- 2,5 ing at least seven atoms. The catalysts are much more effective than those of the prior art, particularly in the preparation of cyclic esters from hydroxy acids and from glycols and dibasic acids higher than malonic. Furthermorewby the use of these catalysts a much higher ratio of monomer to dimer than that obtainableby the method of the above described application may be realized. Many of the compounds herein described have odors rendering them useful in the perfume art. Those containing 15, 16, and 1'1 members in the ring have a pronounced musk-like odor and for this reason are useful as substitutesvfor the active principle of musk and civet.

Eample 6 brassylate, nonamethylene adipate, or hexamethylene azelate to 20 g. of the following perfumes resulted in products having a more pleasant odor yl5 than similar compositions `containing no cyclic ester. The cyclic estersact as powerful flxatives in these compositions and in this respect resemble natural musk (muscone) o rn the lactone from angelica oil.

50, A. An ambre perfume comprising labdanum,

bergamot, and nose. l B. A jasmin perfume comprising benzyl acetate,

linalool, linalyl acetate, and hydroxycitronellal. y C. A -rose perfume comprising geraniol, citronelallal and phenylethyl alcohol.

Addition of 0.1 g.v of 1% solution of ethylene- I claim:

1. In a process for the preparation of a. cyclic ester by depolymerization of the corresponding linear polyester by heating the same under vacuum, the step which comprises heating the linear polyester of w-hydroxypentadecanoic acid at 270 C. in a pressure of 1 mm. for four and a'half hours in contactzwith approximately 1% of stannous chloride.

. 2. In a process for the preparation of a cyclicv ester' by depolymerization of the corresponding linear polyester by heating the same under vacuum, the step which comprises heating the linear polyester of w-hydroxypentadecanoic acid in contact with stannous chloride.

3. In a process for the preparation of a cyclic ester by depolymerization of the corresponding linear polyester by heating the same under vacuum, the step which comprises heating a linear polyester of an o-hydroxy fatty acid said acid having a unit length of at least seven Ain contact with stannous chloride.

4. In a process for the preparation of acyclic ester by depolymerization of the corresponding linear polyester by heating the same under vacuum, the step which comprises heating a linear polyester having structural units of a unit length of at least vseven in contact with stannous chloride. v

5. In a. process for the preparation of a cyclic ester by depolymerization of the corresponding linear'polyester by heating the same under vacuum, the step which comprises heating a linear iron, cobalt, and tin, said elements being in the i divalent state.

6. In a process for the preparation of a cyclic l ester by depolymerization of the corresponding linear polyester by heating the same under vacuum, the step which comprises heating alinear polyester incontact with cobaltous chloride.

'7. In a process for the preparation. of a cyclic ester by depolymerization of the corresponding linear polyester by heating the same under vacuum, the step which comprises heating a linear y polyester in cbntact with magnesium chloride.

8. In a process for the preparation of a cyclic ester by' depolymerization of the corresponding .linear polyester by heating the same under vacuum, the step which comprises heating a linear' polyester of an ll-hydroxy fatty acidV said' acid having a unit length of at least seven in contact with magnesium chloride.

9. Ina process for the preparation of a cyclic ester bny depolymerization of the corresponding linear polyester by heatirg the same under vacul um, the step which comprises heating'the linear polyester of w-hydroxydecanoic acid in contactwith magnesium chloride.-

f EDGAR W. SPANAGEI... 

